The technical field of this invention is that of nondestructive materials characterization, particularly quantitative, model-based measurement of bulk material and surface condition for flat and curved parts. Measurement of bulk material condition includes measurement of changes in material state caused by fatigue damage, plastic deformation assessment, residual stress, applied loads, and processing conditions. It also includes measurement of material states such as porosity, alloy type, moisture content and temperature. Measurement of surface condition includes roughness, displacement of relative position, coating thickness and coating condition. Each of these also include detection of electromagnetic property changes associated with the presence of single or multiple cracks.
The methods for measurement include the use of quasistatic fields, electromagnetic (magnetometers and dielectometers) or thermal, that are described by diffusion equations, as opposed to alternative techniques that are described by wave equations. For example, magnetometers have been used to measure foil thicknesses, characterize coatings, and measure porosity, as well as to measure material property profiles as a function of depth into a part, as disclosed in U.S. Pat. Nos. 5,015,951 and 5,453,689. Dielectometers with multiple electrode spacings have been used to measure profiles of properties such as moisture and porosity using methods disclosed in U.S. Pat. No. 4,814,690.